The present invention relates to integral skin polyurethane foams. The present invention particularly relates to all-water-blown integral skin polyurethane foams.
Integral skin polyurethane foams are used in a wide variety of applications. For example, such foams have been found useful in applications such as furniture and automobile manufacturing. Integral skin polyurethane foams have been found to be particularly useful in the production of automobile steering wheels, spoilers, arm rests, head rests and the like.
The "integral skin" of integral skin polyurethane foam is a tough resilient layer covering the foam interior of objects made of integral skin polyurethane foam. In conventional integral skin polyurethane foams, the skin is formed when, during the foaming process, a reaction admixture typically including CFC-11 is placed into a closed mold. A reaction exotherm causes the CFC-11 to vaporize and separate from the reaction admixture. The CFC-11, upon coming into contact with the comparatively cool mold wall in the presence of the comparatively higher pressure inside the mold, condenses. The liquid CFC-11 on the mold wall causes the cell layer adjacent to the mold wall to collapse, forming the "integral skin". The integral skin of integral skin polyurethane foam can have desirable appearance, touch and durability.
Foams are prepared by frothing a liquid matrix. In preparing a foam, a source of vapor or gas must be provided in order to froth the liquid matrix. Materials which produce or act as these sources of gas or vapor are called blowing agents. A blowing agent is a material which vaporizes or otherwise produces gas during the forming of a foam and thereby serves to reduce the density of the foam. Chlorofluorocarbons have long been used as blowing agents for flexible polyurethane foams. However, due to environmental considerations, the use of chlorofluorocarbons has been increasingly discouraged and use of alternative blowing agents has been found to be desirable.
An example of an alternative type of blowing agent is carbon dioxide. Foams produced from formulations having blowing agents which generate carbon dioxide are considered environmentally superior to foams prepared utilizing only chlorofluorocarbon blowing agents. Water reacts with isocyanates in integral skin polyurethane foam formulations to produce carbon dioxide and is an example of a carbon dioxide producing blowing agent.
While it has been found desirable to reduce the use of chlorofluorocarbon blowing agents, it has not always been trouble-free to do so. Chlorofluorocarbons often contribute to the physical properties of the foams produced therewith. For example, foams produced from formulations having carbon dioxide generating blowing agents rather than chlorofluorocarbon blowing agents often have poorer dimensional stability. Therefore, it would be desirable in the art to prepare a water-blown integral skin polyurethane foam with dimensional stability similar to that of conventional integral skin polyurethane foams.